The use of smallints is limited by the number of entries in your data. If you have more than 64K entries, smallints are a non-starter. Since you mentioned that you are in a "datacenter", I suspect that your tables are larger than this. It sounds like, though you have not said so explicitly, that your current schema uses GUIDs as unique (primary?) keys and they are used as the basis for foreign keys. A case can be made that using GUIDs in this way is less than ideal. They are wider than an int or smallint which would impact their use in indexes. How many entries do you have in your tables?

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